Trap onbeforeunload when event fired (attempt to fix FS#2196)

lib/scripts/edit.js

@@ -320,9 +320,11 @@ addInitEvent(function (){
 
     // reset change memory var on submit
     addEvent($('edbtn__save'), 'click', function(){
+        window.onbeforeunload = '';
         window.textChanged = false;
     });
     addEvent($('edbtn__preview'), 'click', function(){
+        window.onbeforeunload = '';
         window.textChanged = false;
         window.keepDraft = true; // needed to keep draft on page unload
     });